Food and beverage cans are commonly fabricated from aluminum sheet material which is made from aluminum-magnesium alloys such as 5042 and 5182 (AA series) that are heat tempered. The aluminum alloy sheet is normally conversion coated with a solution containing chromium and phosphate before being coated with a polymer such as polyvinylchloride. Because of environmental concerns, there is a need to replace the chromium in this conversion coating.
Apatite is a form of calcium phosphate occurring naturally in the earth's crust. It is a biocompatible mineral that is the main constituent of human teeth and bones. Accordingly, apatite is considered a viable alternative to presently-used chromium phosphate conversion coatings.
It is a principal objective of the present invention to provide a biocompatible coating suitable for use on aluminum sheet.
A related objective of the invention is to form an adhering coating of biocompatible apatite on aluminum sheet using interfacial reactions.
A further objective of the invention is to provide a rapid, commercially useful process for forming the apatite coating on aluminum sheet.